DESCRIPTION (Adapted from the Summary): This proposal aims at defining the interactions that the retroviral structural proteins (Gag) make with each other and with other viral components to form infectious virus particles. Of particular interest is the mechanism by which Gag proteins oligomerize to form virions. Analysis will include the structures of Gag monomers, interactions made between Gag proteins, and Gag-RNA associations. To this end, biophysical and molecular approaches will be applied to determine the virus particle structure. Two specific approaches are proposed. The first utilizes purified histidine-tagged retrovirus Gag proteins and derivatives to make two dimensional and helical proteins and protein plus RNA arrays on lipid monolayers, bilayers, and rod structures containing novel nickel-chelating lipids. Arrays will be analyzed to define Gag and RNA interactions by image enhancement-electron diffraction methods. Gag-RNA binding studies will be performed to identify factors required for specific encapsidation of viral RNAs. The second approach utilizes wild type and mutant virus particles to evaluate their effects on particle assembly and structure. Cysteines will be substituted into the Gag protein and used in crosslinking studies. This will be used to identify proteins which bind to the Gag major homology region (MHR) and the Fv1 N/B tropism determinant.